The term “ophthalmologic apparatus” collectively means equipments used in the ophthalmology field. Examples of the ophthalmologic apparatus include an ophthalmologic imaging apparatus for imaging a subject's eye, an ophthalmologic examination apparatus for optically examining a subject's eye, and an ophthalmologic treatment apparatus for treating a subject's eye. Typical examples of the ophthalmologic imaging apparatus include a fundus camera, an optical coherence tomography (OCT) apparatus, a scanning laser ophthalmoscope (SLO), a slit lamp microscope, a surgical microscope, and the like. Typical examples of the ophthalmologic examination apparatus include a refractometer, a keratometer, a corneal topographer, a visual field test equipment, a wave-front analyzer, a specular microscope, a subjective eye examination apparatus, a tonometer, and the like. Typical examples of the ophthalmologic treatment apparatus include a laser therapy equipment, a cataract surgical equipment, a vitreous body surgical equipment, and the like.
Some ophthalmologic apparatuses perform the focusing of the optical system on a subject's eye. For example, to capture an image of the fundus of the eye, the ophthalmologic apparatus performs focusing on the fundus. The focusing is performed manually or automatically. In any case, an indicator (focusing indicator) is used to figure out the current focus state. As a typical example of the focusing indicator may be cited a split indicator. The split indicator is formed of a pair of light fluxes projected on the fundus, and a positional relationship between projection images of them indicates the current focus state. A user or the ophthalmologic apparatus moves a focusing lens such that two projection images are in a predetermined positional relationship to adjust the focus of the optical system on the fundus.
The focusing with the use of such a focusing indicator requires that both the projection images be recognizable. However, if the subject's eye has a small pupil, light fluxes projected toward the fundus and those reflected from the fundus are blocked by the iris, and the requirement may not be fulfilled. For example, Japanese Unexamined Patent Application Publication No. 2008-278914 discloses a method of automatic focusing for the case where one of the projection images cannot be detected. According to the method, the position of a split indicator (projection image) with respect to a fundus image is stored in advance, and focusing is performed such that one of split indicators, which is recognizable, is located in the stored position.
The conventional automatic focusing method is applicable when at least one of the indicators is recognizable. However, if both the indicators cannot be detected, manual focusing is required. Especially, when the pupil diameter is very small (e.g., 3.5 mm or less), any indicator is likely to be not recognizable.